Bruce N. Wilkie

Selection for high immune response: an alternative approach to animal health maintenance?

To test the hypothesis that variation in ability to respond immunologically correlates with health, Yorkshire pigs were bred for high (HIR) and low (LIR) antibody (Ab) and cell-mediated immune response (CMI). Selection was based on standardized measures of Ab (secondary response to hen egg white lysozyme, serum IgG concentration) and CMI (cutaneous delayed-type hypersenstivity to purified protein derivative of tuberculin after immunization with bacillus Calmette-Guérin and in vitro lymphocyte response to Con-A). Differences in Ab and CMI by line were not restricted to the antigens used in the selection. Antibody response to vaccines was highest in HIR and non-responders were restricted to LIR pigs. The HIR pigs had the best rate of weight gain. After infection with Mycoplasma hyorhinis, HIR developed more severe arthritis and less polyserositis. Differences were associated with variation in cytokine message in joint-related cells. Following exposure to attenuated transmissible gastroenteritis virus, natural killer cells of the LIR pigs but not of HIR or control lines, were unresponsive. Genetic selection for Ab and CMI may provide health and productivity advantages and complement traditional health-maintenance methods.

Use of estimated breeding values in a selection index to breed Yorkshire pigs for high and low immune and innate resistance factors

Abstract A random bred population of Yorkshire pigs (Go) was characterized using fourteen various indicators of immune and innate resistance. Based on initial heritability estimates and correlations between these traits, two measures of antibody (serum IgG, and antibody response to HEWL), and cellular activity (blastogenic response to Con A and cutaneous DTH to BCG/PPD), and one indicator of innate monocyte function (uptake and killing of S. typhimurium) were chosen as breeding criteria to be used in a composite selection index. Based on these five traits a combined estimated breeding value (EBV) was calculated for each animal and pigs were assigned to High, Low or Control breeding groups. Approximately 120 first generation piglets (G1) were then similarly evaluated. Based on Go plus G1 heritability estimates were 0.25, 0.23, 0.08, 0.08 and zero for secondary antibody response to HEWL, blastogenic response to Con A, cutaneous DTH to BCG/PPD, serum IgG, and monocyte function, respectively. Least squares me...

Control of immunoglobulin isotype production by porcine B-cells cultured with cytokines.

Cytokines regulate immunoglobulin (Ig) isotype production following the Th1/Th2 paradigm, derived from studies of inbred mice. In pigs, it is not known which, if any, Ig isotypes may reflect a Th1/Th2 response. To evaluate this, purified porcine CD21(+) B-cells were co-cultured with Staphylococcus aureus Cowan strain 1 or Escherichia coli lipopolysaccharide as B-cell mitogens together with recombinant human IL-2, and recombinant porcine (rp) interferon (IFN)-gamma, IL-12 or IL-10. While the mitogens increased B-cell proliferation, cytokines had no additional effect. A quantitative competitive enzyme-immuno assay was used to measure concentrations of porcine IgM, IgG(1) and IgG(2) in B-cell culture supernatants. In vitro, porcine B-cells produced IgG(2), 106 +/- 17.3 microg/ml; IgG(1) 107 +/- 38.3 microg/ml and IgM 25.6 +/- 8.45 microg/ml. In some individuals, Th1 cytokines such as rpIFN-gamma and IL-12, enhanced IgG(2) in the face of low concentrations of IgG(1). Furthermore, individual responses, in some cases, tended to be diametrically opposed, reminiscent of previously documented categorical immune responses in pigs such that some individuals produced high concentrations of IgG(1) in response to the various doses of rp cytokines, while others produced lower concentrations. Pigs may generate a high IgG(1):IgG(2) ratio in response to rpIL-10, and possibly to other Th2-associated cytokines. However, B-cell response to rp cytokines in vitro exhibits marked variation by pig, a feature that is likely a function of highly variable individual genotypes and their interaction with complex environments.

Mycoplasma hyorhinis infection of pigs selectively bred for high and low immune response.

Pigs have been selected for high (H) or low (L) combined antibody and cell-mediated immune response to test the high immune response phenotype as a candidate for an indirect approach to improving health and productivity in livestock. Mycoplasma hyorhinis infection was induced in H and L pigs of the 4th generation of selection to test the hypothesis that immune response lines differ in response to infection. The major disease sign, arthritis, was more severe in the H pigs both clinically and at necropsy. M. hyorhinis was isolated at higher colony counts from synovial fluids of the H pigs. In contrast, pleuritis and peritonitis were less severe in pigs of the H than those of the L line. Pericarditis, although less in H than L pigs, did not differ significantly by line. Synovial fluid antibody to M. hyorhinis did not differ by line but H pigs produced serum antibody earlier and to a higher titre than did L pigs. Selection for H or L immune response therefore alters response to M. hyorhinis, however there is no indication of a consistent line-related health advantage.

Interferon-alpha and haptoglobin in pigs selectively bred for high and low immune response and infected with Mycoplasma hyorhinis

Pigs selected for high (H) or low (L) combined antibody and cell-mediated immune response were infected with Mycoplasma hyorhinis. Following the infection, arthritis was more severe in the H pigs, while pleuritis and peritonitis were more severe in the L pigs. Since Mycoplasma infections in pigs often cause just mild signs, indicators of the inflammatory response may aid diagnosis of such infections. In addition, data about the genetic influence on inflammatory response indicators are scanty in the pig. The objectives of the study were therefore: firstly, to determine interferon-alpha (IFNalpha) and haptoglobin in M. hyorhinis infected pigs and, secondly, to investigate if the inflammatory response as determined by these indicators was influenced by genetic selection. There was no consistent increase of IFN-alpha in serum following infection. The serum haptoglobin concentration started to increase 3 days post-infection and there was no difference between the two breeding lines. Hence, M. hyorhinis infection in pigs is reflected in increased serum haptoglobin concentration, but no effect of the magnitude of the inflammatory response on this indicator by selection for high or low immune response was observed.

Antibody response to Actinobacillus pleuropneumoniae antigens after vaccination of pigs bred for high and low immune response

To enhance inherent general resistance to infectious diseases an indirect strategy of selective breeding for multiple immune response traits representing both antibody and cell-mediated immune response has been pursued over several generations in pigs. High and low response lines differ significantly not only in response to antigens included in the estimated breeding values upon which the selection was based, but also to other antigens. To test whether or not the lines also differed in antibody response to vaccination, high and low response pigs were given a commercial Actinobacillus pleuropneumoniae vaccine, and their serum antibody to three constituent antigens, carbohydrates (CHO) 1 and 5 and lipopolysaccharide (LPS) 1 was measured by enzyme immunoassay. The high line had significantly (P < or = 0.05) more antibody to all antigens except at day 28 to CHO antigen 5. The frequency of non-response to vaccination was also less in the high response pigs to CHO antigen 1 (P < or = 0.01) and to the LPS antigen (P < or = 0.06) but not to the CHO antigen 5. Based upon these observation it is concluded that the high immune response pigs are more responsive to the commercial vaccine than are the low response pigs and that the strategy of altering population immune response by multi-trait selective breeding may be useful in facilitating vaccine-based health management programs for livestock.

Cytokine mRNA expression in leukocytes of efferent lymph from stimulated lymph nodes in pigs

To test the hypothesis that characteristic cytokine responses occur in stimulated porcine lymph nodes (LNs), lymph node efferent ducts were surgically cannulated. Efferent lymph (EL) leukocytes were collected before and after stimulation of LNs with mitogens [bacterial lipopolysaccharide (LPS) or phytohemagglutinin-P(PHA-P)] and antigens [hen egg white lysozyme (HEWL) or purified protein derivative of tuberculin (PPD)]. Cytokine mRNA expression was evaluated by quantitative reverse transcription polymerase chain reaction (Q-RT-PCR). Interleukin (IL)-1alpha was predominantly produced after all stimuli except for HEWL after which tumour necrosis factor (TNF)-alpha message was dominant. None of the stimuli induced message for IL-2, IL-4 or IL-8. Other cytokine mRNAs were produced in variable amounts and percentage of overall production of each cytokine message was in the following descending rank: LPS: IL-1alpha, TNF-alpha, interferon (IFN)-gamma, IL-10, IL-12-p35, IL-6, IL-12-p40 and TNF-beta; PHA-P: IL-1alpha, TNF-alpha, IL-10, IFN-gamma, IL-12-p40 and TNF-beta; HEWL: TNF-alpha, IL-1alpha, IFN-gamma, IL-10, IL-6, IL-12-p40, TNF-beta and IL-12-p35 and PPD: IL-1alpha, IFN-gamma, TNF-alpha and IL-10. Time course response of cytokines revealed early (IL-1alpha, 10, TNF-alpha) and intermediate (IL-12-p40, TNF-beta, IFN-gamma) responses for PHA-P and early (IL-1alpha, 6, 10, IL-12-p35, IL-12-p40, TNF-alpha), intermediate (TNF-beta, IFN-gamma) and late (IL-1alpha, 6) for LPS. Cytokine mRNA response induced by HEWL was early (IL-alpha, IFN-gamma), intermediate (IL-10, IL-12-p40, TNF-beta), late (IL-1alpha, IL-12-p35) and very late (IL-1alpha, 6, 10, IL-12-p40, TNF-alpha). In Bacillus Calmette-Guérin (BCG) sensitized pigs, stimulation of LNs with PPD induced message for IL-1alpha, 10, TNF-alpha and IFN-gamma which peaked at 24h. Cytokine mRNAs varied by stimulus and differed for antibody and cell-mediated immune response.

The influence of the swine major histocompatibility genes (SLA) on variation in serum immunoglobulin (Ig) concentration

Variation in serum IgG and IgM concentration was determined in three homozygous SLA-defined strains of miniature swine (SLAa, SLAc and SLAd) and one recombinant strain SLAg (ABcDd) as part of a study of SLA and other genetic effects on immune response. Data were obtained from 119 8-week-old piglets from 29 litters by 12 sires and analyzed using a SAS linear model for the effects of SLA haplotype, sire, dam, litter, sex, season of birth and sow parity. SLA haplotype (P less than 0.10) and other genetic effects due to sire (P less than or equal to 0.001) and dam (P less than or equal to 0.002) contributed to the variation in serum IgG concentrations. Season of birth and sow parity also affected IgG concentration as did litter effects. Least squares mean comparisons indicated that pigs of the dd, dg and gg haplotypes had significantly higher serum IgG than did pigs of the other haplotypes. Heritability estimates for IgG, calculated by paternal half-sib correlation, ranged from 0.31 to 0.27, indicating that selection for increased serum IgG concentrations would be possible. For serum IgM concentrations, only the effect of litter was significant at P less than or equal to 0.001 and P less than or equal to 0.009 by the radial immunodiffusion test read at 24 or 48 h. Since sire variance components estimates were negative, heritabilities were not calculated for IgM and are assumed to be zero.

Antibody avidity in Yorkshire pigs of high and low immune response groups.

Avidity indices of antibody to hen egg-white lysozyme (HEWL) were measured by chaotropic ion (SCN-) elution enzyme-linked immunosorbent assay (ELISA) in pigs grouped as high, control or low for various immune and innate resistance-related traits. The avidity index was the molar concentration of SCN- required to reduce by 50% the ELISA optical density value for a given serum. The index was independent of the amount of antibody. Eight- to ten-week-old Yorkshire pigs were immunized with HEWL and serum antibody measured by ELISA as one of five traits used to assign them to high, low or control response groups. Serum antibody avidity for HEWL was evaluated on Day 14 and Day 30 after primary (Day 0) and secondary (Day 14) immunization. The effects of response group, gender, litter, serum IgG concentration and anti-HEWL antibody on avidity were determined using a linear model. Antibody avidity indices varied amongst individuals. Mean avidity indices for sera collected on Days 14 and 30 were 0.61 +/- 0.43 and 1.22 +/- 0.56, with maximum indices of 2.64 and 2.86 respectively. Avidity of secondary response antibody was significantly higher (P less than or equal to 0.05). Pigs of the high response group had significantly higher secondary antibody avidity than those of the control (P less than or equal to 0.08) and low groups (P less than or equal to 0.01). Avidity index was positively correlated with antibody to HEWL on Days 14 and 30 but not to preimmunization serum IgG concentration or to other measured traits.

Effect of selection of swine for high and low immune responsiveness on monocyte superoxide anion production and class II MHC antigen expression.

Monocyte function was investigated in second (G2) and third (G3) generation pigs selected for high and low antibody and cell-mediated immune responsiveness. In groups of pigs from the high-and low-immune response lines, monocyte release of superoxide anion (O2-) was assayed in response to phorbol 12-myristate-13-acetate and expression of the Class II-MHC (MHC-II) antigens SLA-DR and SLA-DQ, determined using flow cytometry. Analysis of variance using a linear model demonstrated no significant intergroup differences in O2- production by lymphokine-activated monocytes from G2 pigs. In G3 pigs, there were no significant intergroup differences in the percentage of MHC-II+ cells or in the density of expression of either SLA-DR or SLA-DQ. In individual pigs, monocyte SLA-DR and SLA-DQ expression was similar in terms of the percentage of MHC-II+ cells and in the magnitude of MHC-II expression. Litter contributed significantly to variation in monocyte O2- production in G2 pigs (P < or = 0.005) and SLA-DQ (P < or = 0.01) expression. Although the lines differed significantly in correlates of antibody and cell-mediated immune response, there was no apparent effect of selection for high and low immune responsiveness in swine on monocyte O2- production and MHC-II expression.